THE "PERFECT ( being horizontal ) TRIM" HOAX

[tr3a]

We metabolize O₂. Our O₂ sensors measure how much O₂ is left in the system and injects that through a solenoid, or the diver does it. The rest of the gas is scrubbed with sof-no-lime to remove the CO₂, and we breathe the recycled mixture. That's why we call it CC or Closed Circuit. The most we can use while breathing is 21%. But, we also use some "dil" for our BC or if we vent any of our loop, so it's usually a bit less. Does that make sense?

 

[scubadada]

That's what I said, > 6L/min. The best air consumption rate I've ever achieved was 6.4L/min with a baby cylinder, but usually I average 7.5-8.5L/min on most dives on normal AL80. 15L/min is the average consumption rate of SB divers according to survey, and I'm gonna call SB divers more experienced than average. All of my tech instructors average 14-16L/min too. I struggle to build a buddy team with consistent single digit air consumption rate on all dives. I have only been able to do that with Asian divers.

It has nothing to do with my question though. I was just confused about OC air vs CC O2 consumption in another comment. 0.8L/min isn't single digit, its 1/10 of a single digit, 1/10 of my typical consumption, 1/20 of an average experienced diver consumption. Hence my confusion.

Hi @dumpsterpurrs

Your gas consumption is very low. You are correct, in the gas consumption poll, the average respondent has a gas consumption of 14.2-16.5 L/min or 0.5-0.59 cu ft/min. Your lowest gas consumption of 6.4 L/min corresponds to 0.22 cu ft/min. Your average of 7.5-8.5 L/min is only 0.26-0.30 cu ft/min. I don't remember if I asked if you had voted in the poll. You would be among the 12 divers in the lowest gas consumption category. No wonder you cannot find many divers to match your gas consumption. I would be a gas hog relative to you and my average RMV over the last 5 years is 0.34 cu ft/min or 9.6 L/min.

Thread 'Average Gas Consumption'

Jul 3, 2016

There has been extensive discussion lately regarding average gas consumption. A poll may help give us a better idea of what the normal distribution of RMVs is.

1 cu ft = 28.32 liters
1 liter = 0.035 cu ft

<0.3 cu ft/min = <8.5 l/min
0.3-0.39 cu ft/min = 8.5-11.0 l/min
0.4-0.49 cu ft/min = 11.3-13.9 l/min
0.5-0.59 cu ft/min = 14.2-16.7 l/min
0.6-0.69 cu ft/min = 17.0-19.5 l/min
0.7-0.79 cu ft/min = 19.8-22.4 l/min
0.8-0.89 cu ft/min = 22.6-25.2 l/min
0.9-0.99 cu ft/min = 25.5-28.0 l/min
>1.0 cu ft/min = >28.3 l/min

• scubadada
• Replies: 581
• Forum: Basic Scuba

• 

 

[dumpsterpurrs]

@scubadada Yes I've voted a long time ago. Love that thread btw, it's the survey where I got the 14-16L number from. The data helped me improved my air consumption.

I'm actually far from the lowest air consumption in my group. Asian girls really don't breathe, even the ones who aren't that extremely experienced. Any moderately-skilled, not completely new (~50-70 dives and up) Asian female diver I know has freakishly low air consumption. My buddy's "reef name" (like a hiker's trail name ) is T-BAR, because her name starts with T and she pretty much always finishes dives with at least 100 bars in her cylinders. The hand signal for 100 bar looks like you're making a T ^^

 

[scubadada]

Hi @dumpsterpurrs

T, half tank

 

[lexvil]

@scubadada Yes I've voted a long time ago. Love that thread btw, it's the survey where I got the 14-16L number from. The data helped me improved my air consumption.

I'm actually far from the lowest air consumption in my group. Asian girls really don't breathe, even the ones who aren't that extremely experienced. Any moderately-skilled, not completely new (~50-70 dives and up) Asian female diver I know has freakishly low air consumption. My buddy's "reef name" (like a hiker's trail name ) is T-BAR, because her name starts with T and she pretty much always finishes dives with at least 100 bars in her cylinders. The hand signal for 100 bar looks like you're making a T ^^

I refer to such divers as self propelled pony’s

 

[dmaziuk]

I've been reading a bit more and it seems in the OC context the gas we breathe out is around 16% O2, meaning we use up around 5%. 5% is 1/20 the total volume of the air breathed. Maybe that explains why the CC O2 consumption rate could be more or less somewhere around 1/20 the OC air consumption rate?

O2 "consumption rate" is the same everywhere (exertion level etc. notwithstanding). The difference is that on space station, submarines, and CCR, exhaled gas doesn't "fly away" into the outside world.

 

[Blackcrusader]

Hi @dumpsterpurrs

Your gas consumption is very low. You are correct, in the gas consumption poll, the average respondent has a gas consumption of 14.2-16.5 L/min or 0.5-0.59 cu ft/min. Your lowest gas consumption of 6.4 L/min corresponds to 0.22 cu ft/min. Your average of 7.5-8.5 L/min is only 0.26-0.30 cu ft/min. I don't remember if I asked if you had voted in the poll. You would be among the 12 divers in the lowest gas consumption category. No wonder you cannot find many divers to match your gas consumption. I would be a gas hog relative to you and my average RMV over the last 5 years is 0.34 cu ft/min or 9.6 L/min.

@dumpsterpurrs

This is the third dive I did today. It was against a current for the first 25 minutes of the dive. Our guide here has separated myself and my dive buddy from others so we can do some dives others cannot complete without being seriously low on air. I started with 200 bar finished with 70 bar.

On my best dives with no current and just chilling I use around .6 bar/min. Todays dive was .86 which is still pretty reasonable. My guide had 230 bar in his tank and used about 20 bar more than I did. My dive buddy was around 10 bar more he finished with 60 bar.

I'm unusual in that I am a large white dude with good gas consumption.

 

[dumpsterpurrs]

@dumpsterpurrs

This is the third dive I did today. It was against a current for the first 25 minutes of the dive. Our guide here has separated myself and my dive buddy from others so we can do some dives others cannot complete without being seriously low on air. I started with 200 bar finished with 70 bar.

On my best dives with no current and just chilling I use around .6 bar/min. Todays dive was .86 which is still pretty reasonable. My guide had 230 bar in his tank and used about 20 bar more than I did. My dive buddy was around 10 bar more he finished with 60 bar.

I'm unusual in that I am a large white dude with good gas consumption.

View attachment 899491

Is this reply meant for @scubadada or me? He's the one collecting data, not me, I just use his. He probably would like it if you could vote in his poll. Your SAC rate is around 9.7L/min.

If you and @scubadada would like to dive with a bunch of Asian girls let me know but I personally do prefer a slightly more flat/straight/less sawtooth profile. I'm quite physically weak with small ear canals, this dive profile would send me straight to a nap after, and repeating it would make my ears a bit sore.

 

[rx7diver]

@dumpsterpurrs,

I'm not sure everyone determines SAC rate (RMV) the same way. (So, not everyone is talking about the same thing when they refer to SAC rate, I think!) I learned to determine SAC rate(s) for dive planning a very long time ago using the following approach: Wearing the gear you intend to use for the upcoming dive, drop down to 20 ffw or so, get neutral, swim--fin--horizontally for a few minutes using your usual slow finning pace, and reverse course and fin back to the start. Using your cylinder pressures from the start and end of your "swim" for your particular cylinder(s), and your elapsed swim time (and the depth of your swim), compute your SAC rate.

Obviously, you'll compute different SAC rates for different gear configurations.

And the SAC rate you compute using the above approach is your working SAC rate. Your resting SAC rate (e.g., your SAC rate when you're comfortable, in calm seas, hanging onto the down line at your 20 ffw safefy stop) will, of course, be different than your working SAC rate.

FWIW, your best 6.4 L/min (= 0.23 ft^3/min) SAC rate is well below even my best resting SAC rate when I was in my best shape for diving, ~35 years ago! (I am male, 6'2", and I was ~230 lbs ~35 years ago.)

rx7diver

 

[dumpsterpurrs]

@dumpsterpurrs,

I'm not sure everyone determines SAC rate (RMV) the same way.

Exactly! Since I only do single AL80 tropical dives these days, I do have different *planning* SAC rate that I use to plan fun dive for myself (11L/min for the normal portion and 15L/min for emergency contingency), actual *working* SAC rate when I lead dives or wrestle with my kid and/or camera (8.5-10L/min), actual *normal* SAC rate on an average fun dive in the typical current conditions of places like Indonesia, Puerto Galera, Richelieu Rock, etc with no camera or just minimal wide angle videoing (7.5-8.5L/min - this is *the* official SAC rate I use because it's almost all of my diving), and then there's also the actual *resting* SAC rate of gentle drift or lazy muck dives when I do nothing but chill and get high from staring at the reef (7-7.5L/min, 6.4L was an extreme outlier only achievable on baby cylinders, not typical AL80, definitely not SS100).

My sidemount SAC with 2 AL80's is a little bit more. I don't have my logbook here, but I think around 9-11L for normal dives? I'm still very very inexperienced, and rarely sidemount with 2 cylinders anymore, so it probably will either stay the same or get worse over time.

I normally include all gas used during a dive from start to finish in my calculation because the little used for bcd throughout the dive and dsmb at the end don't change my calculations by much. I'm too lazy to do the proper method you described but I don't calculate SAC on dives I make jacuzzi bubbles for my buddies or *ahem* flush my very thick semi dry suit xD

Btw I hope my planning SAC numbers sound about prudent enough to people. I must admit I only picked those numbers because it makes the math easier...